When returning HTML from a helper, you should return a
Handlebars SafeString if you don't want it to be escaped
by default. When using SafeString all unknown or unsafe data should
be manually escaped with the escapeExpression method.

You can also pass a simple String, number, or boolean as a parameter to Handlebars
helpers.

{{{link "See more..." story.url}}}

In this case, Handlebars will pass the link helper two parameters:
the String "See more..." and the result of evaluating
story.url in the current context.

Subexpressions

Handlebars offers support for subexpressions, which allows
you to invoke multiple helpers within a single mustache, and
pass in the results of inner helper invocations as arguments
to outer helpers. Subexpressions are delimited by
parentheses.

{{outer-helper (inner-helper 'abc') 'def'}}

In this case, inner-helper will get invoked
with the string argument 'abc', and whatever
the inner-helper function returns will get
passed in as the first argument to outer-helper
(and 'def' will get passed in as the
second argument to outer-helper).

Whitespace Control

Template whitespace may be omitted from either side of any mustache statement by adding a
~ character by the braces. When applied all whitespace on that side will be
removed up to the first handlebars expression or non-whitespace character on that side.

Escaping

Handlebars content may be escaped in one of two ways, inline escapes or raw block helpers.
Inline escapes created by prefixing a mustache block with \. Raw blocks are
created using {{{{ mustache braces.

\{{escaped}}{{{{raw}}}}
{{escaped}}{{{{/raw}}}}

Raw blocks operate in the same manner as other block helpers
with the distinction of the child content is treated as a literal string.